A copper damascene interconnect of a high-performance LSI is normally formed by chemical mechanical polishing (hereinafter may be referred to as “CMP”). Specifically, a desired interconnect is formed by filling a groove or the like formed in an insulating material with an interconnect material, and removing unnecessary interconnect material by chemical mechanical polishing.
A chemical mechanical polishing process discharges polishing liquid waste (hereinafter may be referred to as “CMP liquid waste”) that contains a chemical mechanical polishing aqueous dispersion used for CMP, polishing waste produced from the material of each layer of a semiconductor device formed on a wafer (i.e., polishing target), polishing waste produced from a polishing pad, etc. Polishing waste contained in the CMP liquid waste damages the polishing target surface of each layer of the semiconductor device, and the polishing performance deteriorates when polishing waste has been accumulated. Therefore, CMP liquid waste is not recycled as the chemical mechanical polishing aqueous dispersion. In recent years, the amount of chemical mechanical polishing aqueous dispersion used has rapidly increased along with an increase in the degree of integration of semiconductor devices. Therefore, a reduction in the amount of CMP liquid waste has been desired.
The most efficient CMP liquid waste reduction method is to recycle the chemical mechanical polishing aqueous dispersion from the viewpoint of reducing environmental impact while reducing the semiconductor device production cost. For example, JP-A-11-10540 discloses technology that recycles the chemical mechanical polishing aqueous dispersion using an ion-removing membrane. JP-A-11-277434 discloses technology that recycles the chemical mechanical polishing aqueous dispersion by dispersing the abrasive grains using a vibrator. JP-A-2000-71172 and JP-A-2001-162534 disclose technology that adds an unused chemical mechanical polishing aqueous dispersion and additives to the used chemical mechanical polishing aqueous dispersion to recycle the chemical mechanical polishing aqueous dispersion. JP-A-2002-170793 discloses technology that removes coarse particles from CMP liquid waste by centrifugation, and uses the collected abrasive grains for a chemical mechanical polishing aqueous dispersion.
However, these recycling systems have a problem in that metal ions produced by polishing an interconnect metal (e.g., copper) are accumulated so that the polishing performance after recycling significantly deteriorates as compared with the initial polishing performance.
In recent years, attempts have been made to apply CMP to planarize a substrate (hereinafter referred to as “electro-optical display substrate”) used to produce an electro-optical display such as a flat panel display (e.g., liquid crystal display (LCD), plasma display panel (PDP), electrochromic display (ECD), electroluminescent display (ELD), and field emission display (FED)). However, since the electro-optical display substrate normally has a maximum dimension of about 1500 to 3000 mm, a large amount of interconnect material must be removed as compared with a semiconductor device substrate. When chemically and mechanically polishing an interconnect material of the electro-optical display substrate, metal ions produced from the interconnect metal during CMP are accumulated in the chemical mechanical polishing aqueous dispersion so that the polishing performance significantly deteriorates as compared with the initial polishing performance.